Aluminum alloy system

ABSTRACT

WROUGHT ARTICLES OF AL-CU-MG ALLOY CONTAINING UP TO ABOUT 5% COPPER AND UP TO ABOUT 2% MAGNESIUM AS THE PRINCIPAL ALLOYING ELEMENTS BY WEIGHT, WITHIN LIMITS EFFECTIVE TO ACHIEVE SUBSTANTIALLY SINGLE PHASE STRUCTURE, AND EXHIBITING IMPROVED FRACTURE TOUGHNESS IN T8XX CONDITION; ALSO, RELATED PRACTICES AND IMPROVED ALLOY COMPOSITIONS FOR MAKING SUCH ARTICLES, INCLUDING PLATE.

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ALUMINUM ALLOY SYSTEM .Filed Aug. 3, 1972 8 Sheets-Sheet 6 VPSP %STRETCH0.2 0.5 0.8 )2.0

2 o a o 6000- B D [l l veraqe'll Tests per Lot D D E n i soun- Co u U oIl l l l l l 0.5 0.6 0.7 0.8 0.9 1.0

Agglied Stress Yiald Strangth F G 6 Short-Transverse Notched FatiguaBahavior o'f lll-148 at an Applied SI'BSS 0f 45 kS. (Laboratory produced1.25 inch thick plate).

S. A. LEVY ALUIINUI ALLOY SYSTEM' Juy 3", 1974 Longitudinal Section,250x, Unetched.

8 Sheets-Sheet '7 VPSP VPSP

MID-148 (X2048) Photomicrographs Illustrating the Relative Levels ofSecond Phase Particles in 202i, 212A, and NID-148.

July 30, 1974 s. A. LEVY 3,826,688

Anuumuu Amm sfsfrmY .Filed Aug. 5, 1972 8 Sheets-Sheet B M11-14s (xzoas)FI G Photornicrographs Illustratng the Relative Levels of Second PhaseParticles in 2024, 2124, and M13-148.

Rolling Plane, lOOX, Unetched.

United States Patent O 3,826,688 ALUMINUM ALLOY SYSTEM Sander A. Levy,Richmond, Va., assignor to Reynolds Metals Company, Richmond, Va.Continuation-impart of application Ser. No. 105,061, Jan. 8, 1971. Thisapplication Aug. 3, 1972, Ser. No. 277,605

Int. Cl. C22f 1/04 U.S. Cl. 148-2 29 Claims ABSTRACT OF THE DISCLOSUREWrought articles of Al-Cu-Mg alloy containing up to about copper and upto about 2% magnesium as the principal alloying elements by weight,Within limits effective to achieve substantially single phase structure,and exhibiting improved fracture toughness in -TSXX condition; also,related practices and improved alloy compositions for making sucharticles, including plate.

This application is a continuation-in-part of applicants prior copendingapplication Ser. No. 105,061, tiled on Ian. 8, 1971.

The present invention relates to improvements in wrought articles madeof an aluminum base alloy containing copper and magnesium as theprincipal alloying elements by weight, in amounts up to about 5% Cu andup to about 2% Mg, including at least 0.3% magnesium and at least about3% total of copper and magnesium; and it further relates to practicesfor making such articles to achieve improved properties, and to alloycompositions of the Al-Cu-Mg type.

Alloy 2024 as currently produced commercially contains a largepercentage of second phase particles, such as (i) 0 phase--CuAl2, (ii) Sphase-AlgCuMg, and (iii) FeMnAlq Cu2FeAl7 is another probable phase.These particles apparently add little to the strength of the alloy, buttend to impair both ductility and toughness. In addition to 3.8% to 4.9%copper and 1.2 to 1.8% magnesium, alloy 2024 contains 0.3 to 0.9%manganese, with iron up to 0.50%, silicon up to 0.50%, chromium up to0.10%, zinc up to 0.251%, others, .05% max. each and 0.15% total,balance aluminum. Thus, there are three major sources of second phaseparticles: the minor addition element Mn, undissolved soluble phasescontaining Cu and Mg, and trace elements such as Si and Fe. Alloy 2124is similar, except for lower maximum amounts of silicon and iron.

As far as the reasons for originally including manganese in 2024 alloyare concerned, it seems to have been generally recognized that Mn tiesup Fe and so avoids the presence of long FeAl3 needles which tend tocause embrittlement. Manganese may also reduce the amount of lCu tied upby Fe, and so increase the availability of Cu for precipitation. Thepresence of manganese also tends to inhibit recrystallization, althoughin other systems it is less elective in this respect than Cr or Zr.Further, manganese contributes to strength of the alloy in two ways, inthat the portion in solid solution has a direct inuence and its effecton recrystallization may also result in increased strength due to thepresence of substructure.

ICC

In connection with previous work on the Al-Zn-Mg-Cu system, especially7075 alloy, it has been noted that various properties are improved byusing prolonged solution heat treatments and limiting the occurrence ofsecond phases by using higher purity (low Si, Fe, and Mn) aluminum basemetal. In trying to apply the same general approach to producing ahomogeneous 2024-type alloy, however, it became apparent that use ofhigh purity aluminum and prolonged homogenization alone would notsuffice.

As regards Al-Cu-Mg alloys in particular, it has been determined inaccordance with the present invention that limitations must be imposedspecifically on the major alloying elements copper and magnesium, inorder to achieve the desired results. Thus, a first aspect of theinvention is providing an aluminum base alloy containing copper andmagnesium essentially within their solubility limit, as indicated by asolidus temperature (incipient melting point) of at least about 945 F.or higher in homogenized condition. This criterion alone distinguishesthe alloys of the present invention from commercial grades of 2024alloy, having a solidus temperature of about 935 F. (Metals Handbook,vol. 1, 8th edition, page 938).

A second aspect of the invention involves controlling the impurity andminor alloying elements to an extent suicient to make possible theattainment of substantially single phase structure. As used herein, awrought article has substantially single phase structure when its VPSP(volume percent second phase) does not exceed 1% on the basis of secondphase particles which are visible and resolvable in unetched conditionunder optical magnification up to 1000x.

As a result of preliminary work it also became apparent that excessivesuppression of the minor alloying element manganese could lead to a lossin strength, impaired ductility, and possibily inferior stress corrosionresistance due to inability to maintain an elongated grain structure.Accordingly, a third aspect of the present invention is that ofproviding Al-Cu-Mg alloys which contain up to about 0.4% manganese in anamount effective approximately to saturate the matrix without producingundesirable amounts of insoluble particles. The use of chromium and/ orzirconium in at least partial replacement of or in addition to manganeseis also contemplated.

The alloy may further include incidental amounts of silicon, iron, zincand titanium, ordinarily in minor fractional amounts each, ashereinafter discussed in greater detail, but is substantially free ofother impurities (Le. typically .05 max. each, 0.15 max. total).

When all of the foregoing considerations are taken into account theresulting wrought articles of Al-Cu-Mg alloy in -T8XX temper not onlyhave suitable homogeneity and more nearly isotropic properties, but alsoexhibit improved fracture toughness at least 50% greater than and up toabout double that of conventional 2024-T857 alloy.

In summary, therefore, a wrought article of Al-Cu-Mg alloy in accordancewith the present invention is characterized compositionally bycontaining up to about 5% copper and up to about 2% magnesium as themajor alloying elements, and upto about 0.4% manganese, within limitseffective to achieve a solidus of 945 F. or higher in homogenizedcondition; and is further characterized and distinguishedbysubstantially single phase structure. Such articles advantageously aremade of alloy compositions atfording a yield strength of at least 45,000p.s.i. in -TSXX temper, preferably at least 52,000 p.s.i. Plate productsof this type may exhibit a short transverse yield strength of about 45to 60 k.s.i., and up to 10% elongation.

Improved alloy compositions of the present invention may include siliconand iron in amounts up to about 0.2% each (typically about .0S-0.3%total), as well as minor alloying additions and incidental elementsincluding, for example, up to about 0.2% titanium, up to about 0.2%

chromium, up to about 0.4% manganese, up to 0.25% or even somewhat morezinc, and up to about 0.25% zirconium; but all of these elements andother impurities ordinarily will not exceed 1% in the aggregate. Suchalloys contain at least about 3% total of copper and magnesium,including at least about 0.6% magnesium, in

order to achieve adequate strength, preferably about 4- 5.5% total of Cuand Mg when maximum strength is desired, with copper typically in therange of about 3-4.5% by weight. Optimum alloys are those containing atleast 1.2% magnesium and less than 3.8% copper, preferably about 2.93.7%Cu and about l.3-1.7% Mg, thus further distinguishing over conventional2024 alloy.

The accompanying FIGS. 1-6l are graphical representations of certaindata discussed in the examples; and FIG. 7 shows a comparison of alloymicrostructures hereinafter described.

The following exemplary practices of the invention are provided forpurpose of illustration.

4 EXAMPLE 1 Ingots of various Al-Cu-Mg alloys prepared for processing inaccordance with method aspects of the present invention weresemicontinuously cast using a CC mold. The majority were lb. ingots witha 3 x 8" cross section. A few 400 1b. ingots (4 x 14) were also used.Differential thermal analysis (DTA) samples were taken from replicatechemical analysis buttons. Chemical analyses were performedspectrochemically and the results are presented in Table I.

The ingots were homogenized in dry air (about -40 F. dew point) for 48hours at about 10 F. below the incipient melting point, as determined byDTA techniques. After homogenization 1A" was scalped from the two largesurfaces of each ingot. The ingots were preheated to 800 F. for rolling.Reductions of 1A per pass were taken, with reheating to 800 F. afterfour passes or when the temperature dropped to 650 F.

The nal heat treatments involved solution heat treatment for 5 hours atabout 10 below the melting point (DTA basis), and cold water quenching.After a one day incubation at room temperature, portions of the platewere stretched 2% or 8%. The 2% stretch plates then were aged for 12hours at 375 F. and the 8% plates for 8 hours at 375 F. A controlledheating rate of 25 F./hr. was used to reach the aging temperature.Tensile (standard .505" for L and LT and compact specimens for ST) andcompact tension KIC specimens were obtained.

Mechanical properties are listed in Table II, for the compositionsindicated by asterisk in Table I.

TABLE I.-ALLOY COMPOSITIONS AND THEIRDSTOIIDUS TEMPERATURES, AS DETER-MINED BY Solidus F.)

Homog- Fe Cu Mn Mg Cr N1 Zn Tl Zr Cast enized 09 3. 83 30 29 01 01 01 164. 23 40 64 01 01 01 17 3.83 .29 .65 01 .01 .01 03 3. 87 19 65 01 01 0203 3. 57 28 73 02 02 02 06 3. 27 27 79 02 02 02 03 3. 19 27 80 02 02 02.02 3.94 .15 .96 .01 .01 .01 .04 3.54 .28 .99 .02 .02 .02 01 3. 87 17 1.04 01 01 01 04 3. 24 27 1. 06 02 02 02 06 4. 15 27 1. 09 02 02 02 02 3.92 29 1. 10 01 01 01 04 4. 02 27 1. 12 02 02 02 05 3. 90 39 1. 22 01 0101 05 4.01 23 1. 22 01 01 01 04 3. 59 28 1. 26 02 02 O2 04 3. 26 27 1.36 02 02 02 06 4. 13 26 1. 37 02 02 02 16 4. 43 33 1. 54 01 01 01 05 3.27 32 1. 66 01 01 01 05 3.87 32 1. 68 0l 01 0l 05 3. 70 34 2. 11 01 0101 04 4. 24 35 1. 56 01 01 01 04 4. 25 40 1. 88 01 01 01 TABLEIll-MECHANICAL PROPERTIES OF HEAT TREATED ALLOYS Direc- Percent; PercentS No. tion stretch UTS Y.S. e1 u I g J'n Fe Zr 24261 ST 2 55.6 44 11.9ST 8 62.4 55.6 9.3 3.83 .65 .29 17 .01 L 2 55. 8 45. 5 12. 1 L 8 62. 858. 3 11. 4

24262 ST 2 51. 3 39. 4 16. ST 8 54. 0 45. 9 12. L 2 51. 4 40. 8 15. L 851. 0 40. 8 14.

24353 ST 2 55.7 43.7 15. ST 8 63. 9 55. 5 12. L 2 55. 1 45. 2 15. L 863. 4 58. 4 14.

23094 L 2 64. 9 55. 3 10. L 8 72. 6 68. 5 9. L 2 62. 6 49. 1 14. LT 260. 8 44. 8 12.

24742 ST 2 62. 6 46. 7 11. L 8 65. 2 53. 0 12. LT 8 66. 2 52. 3 9. ST 804. 6 50. 4 7.

At 0.65% Mg content it may be noted with reference to Table II that theZr-containing alloy (S No. 24353) is as strong as the Zr-free version (SNo. 24261), but exhibits even greater elongation, perhaps due partly toits lower iron content. Also of interest is the relatively high shorttransverse (ST) elongation obtained in both instances.

At the 1% Mg level the Zr-free alloy had higher strength. On the basisof hardness, however, the elect of Zr does not seem significant oneither the rate of aging or the'peak hardness.

Fracture toughness tests of 2t-inch plate in -TSXX temper (2% stretch)indicated that these alloys were so tough as to require platethicknesses of between 1.5 and 1.75 inches for dependable results. Othertests (8% stretch) provided KQ values considered to be within 10% of thetrue KIC, and indicating essentially a doubling of toughness over 2024alloy. Fracture toughness results were determined in accordance withATSM practice E39970T, Part 31, May 1970, pages 911-927.

Although the data given in Table I on incipient melting points includeresults for certain compositions in cast condition, and for others afterhomogenizing treatment, the latter approach has been found more reliableand more definitive in distinguishing the compositions effective for.purposes of the present invention. Such compositions are susceptible tosolution treatment at temperatures higher than conventional 2024 alloy.

The following additional data summarize the results of various tests onlaboratory produced materials, and also on `live plant-produced heats.

IEXAMPLE 2 (I) Chemistry and Processing (a) Laboratory heats-Severallots of laboratory produced materials were prepared from 4 x 14 x 72inch ingots of the following compositions:

Special care was exercised to cool the ingots directly fromhomogenization temperature to the hot rolling temperature (approximately890 F.) to minimize the reprecipitation of second phase particles.Rolling to either 3 or 6 inch plate thickness involved normal 2024practices. Final solution heat treatment was performed at 91.0 t0 925 F.for 3 hours. The plates were stretched immediately after quenching. ForLot I, both 2 and 6% stretch were used and the inal aging time at 375 F.was adjusted according to the level of stretching (see Table VI). Forthe remaining four heats (Table VII) only 3 plate, 2% stretch, and a nalage of 12 to 14 hours at 375 F. were employed.

(II) Mechanical Properties and Fracture Toughness (a) 1.25" laboratoryplate-Tables III and IV present additional data for laboratory producedheats of the subject alloy, for compositions indicated by a double ortriple asterisk in Table I. Typ-ical results for laboratory material aresummarized in FIG. 1, compared t0 2024 alloy.

(b) Thin gage-Kc values and Kahn tear testing.- While the majority oftesting concerned plate products,

some testing of thin gage material was conducted. Eight sheets of therst two compositions (S Nos. 26497 and 26498) were rolled to .080 inchfor plane stress fracture toughness tests, by hot rolling as noted aboveto a thickness of 1A inch, etching and cold rolling to .080 inch.

With some exceptions (as noted) the subsequent thermal treatment ofthese materials involved a 24 hour solution heat treatment at 925 F.`and cold water quenching. After a one day room temperature incubationthe samples were stretched. Those pieces stretched 2% were aged 12 hoursat 375 F., and those stretched 8% were aged 8 hours at 375 F. A 25F./hr. heating rate was used in all cases.

These ingots were stress relieved for 24 hours at 550 F. and then cutinto 24 inch long sections. After homogenizing in dry air (about F. dewpoint) for 48 hours at 925 F., the ingotsections were scalped to 3.25inch thickness and hot rolled at 800 F. Reductions of 1A inch per passwere taken, with reheating to 800 F. after four passes or when thetemperature dropped to 650 F. `Except as otherwise noted these materialswere Afinished at 1.25 inch thickness.

(b) Plant heats-Five plant produced heats were cast as 16 x 60 ingots.The first three involved alloy variations without Zr A) and with Zr(-B). The chemical compositions of these ingots were:

Lot No. Cu Fe Si Mn Mg Ti Zr The results of .080 gage fracture toughnesstests indicate that:

(a) with 2% stretch the alloy is as tough as 2024-T3,

but has about 20 k.s.i. higher yield strength;

(b) with 8% stretch its strength and toughness are comparable to7475T61;

- (c) with 8% stretch there is strength comparable to 2024-T86, as wellas about double its toughness.

Kahn tear tests in both the L-T and T-L directions also showed goodtoughness (see Table V) and only slight directionality of properties.

(c) Plant produced plate-Results for the rst plant heat with two platethicknesses and two levels of stretch are presented in Table VI.Although a substantial improvement occurred with respect to 2024, thefull potential of the alloysystem was not realized until the higheringot homogenization practice was employed, as for the four subsequentheats, cf. Table V111.

(III) Fatigue Fatigue results, for material taken from Lot ILA, arepresented in FIGS. 2-5. These results indicate that the alloy iscomparable to 2024 or 2124 in this property. For the short transversedirection, in laboratory produced material, the alloy has even higherfatigue resistance than 2024 or 2124 (cf. FIG. 6), particularly for thelow cycle (high stress) range.

KQ (K.s.i. lin

el. L-T T-L L-T or (T-L).

Krc VPSP YS Percent (lr.s.i.)

Percent YS el.

(V) Stress Corrosion 2024-T851 specifications require passing 30 days ofalternate immersion in a 3% NaCl solution at 50% of the yield strength,in the ST direction. For alloys of the pres- TABLE III FractureToughness of 1.25" Laboratory Produced Plate A in tigmeg, Direc- UTS 375F. tion (k.s.i.)

TABLE IV Mechanical propertise and fracture toughness ot laboratoryproduced allows with different Zr and/or Mn additions Percent Zr Mn tionUTS 5 ent invention in its preferred operating range (4.05.5% total ofcopper and magnesium, including at least 1.2% Mg and less than 3.8% Cu)most specimens pass a 90 day exposure (cf. Table VII). Many samples alsopass test- 10 ing at 75% of the ST yield strength. The Zr-free alloyapparently is superior to the Zr-containing alloy in stress corrosionresistance.

Percent VPSP stretch For composition see Table I.

S No.

(IV) Elevated Temperature Stability The effect on residual strength ofthe alloy (Lot LA and -B) after exposure for 100 hours at 400 F. ispresented in Table VIII. This property is important particularly forsupersonic aircraft where air friction can cause temperatures to about275 F. It appears that the present alloy has a comparable advantageregarding thermal stability as 2024 with respect to the 7000 series highstrength alloys.

S No.

327.8904133 17.58.16.77.67 9150369115 v0. .L .Ku-5.9m GMGMWMMGBG@659492957 L LT ST L LT ST L LT ST For composition see Table I.

Alloy l Data of Kaufman and Holt-Fracture Characteristics of AluminumAlloys (Paper No. 18).

TABLE VI E or T-L) Plant produced-MDMS (Lotl I) Test Percent Hrs. atdirec- VPSP ness Comp. strength 375 F. tion S. No.

providing an ingot composed of an alloy consisting essentially ofaluminum, copper and magnesium, in amounts up to about 5% copper and upto about 2% magnesium not exceeding their limit of solubility,`including at least 0.3% magnesium and at least 3% total of copper andmagnesium, with no more than one percent total of minor alloyingelements and incidental impurities from the group consisting of silicon,iron, manganese, chromium, zinc, titanium and zirconium, including about.0S-0.3% total of silicon and iron, others up to about 0.4% in the caseof manganese, up to about 0.25% in the case of zinc and zirconium, andup to about 0.2% in the case of chromium and titanium, said alloy beingfurther characterized by a solidus temperature of at least 945 F. orhigher in homogenized condition; heating said ingot to homogenize thealloy; and hot rolling the ingot to obtain a wrought article exhibit- 75ing substantially single phase structure, having a solid y thecombination *ASTM Publication 291.

Finally, in FIG. 7, a comparison is shown between the 60 In conclusion,it has been found that alloy MD-148 tially single phase structureobtained in accordance with the present invention.

(X2048') consisting essentially of aluminum, about 2.9- 65 3.7% copper,about 1.3-1.7% magnesium and about 0.1- 0.4% manganese, adapted forhomogenizing treatment at 940-960 F., is useful in making Wroughtarticles such as hot rolled plate which, in -TSXX temper, exhibit betterstrength than 2219 alloy and better fracture toughness 70 than 2024 and2124 alloys, particularl of a short transverse yield strength of atleast 55 k.s.i. and an L-T plane strain fracture toughness value of atleast 35 k.s.i.\/in., compared to typical values of 22.5 for 2024 alloyand 28 for 2124 alloy.

microstructure of conventional 2024 alloy and a substanf1 1 solutionmatrix of copper and magnesium in aluminum and a volume percent ofsecond phase particles not exceeding one percent based on particles thatare visible and resolvable in unetched condition under opticalmagnification up to 1000 X.

2. The method of claim 1, wherein said processing includes solution heattreating the wrought article.

3. The method of claim 1 wherein said processing includes solution heattreating and artificially aging the wrought article.

4. The method of claim 3 wherein said processing includes cold workingthe solution treated article at least 11/2 prior to said agingtreatment.

5. The method of claim 1 including homogenizini;I the ingot at about940-9\60 F.

6. The method of claim 5 including cooling the homogenized ingotdirectly to hot rolling temperature.

7. A wrought article exhibiting substantially single phase structurehaving a solid solution matrix of copper and magnesium in aluminum and avolume percent of second phase particles not exceeding one percent basedon particles that are visible and resolvable in unetched condition underoptical magnification up to 1000x, said article being composed of analuminum base alloy consisting essentially of aluminum, copper andmagnesium, in amounts up to about 5% copper and up to about 2% magnesiumnot exceeding their limit of solubility, including at least about 0.3%magnesium and at least about 3% total of copper and magnesium, byweight, up to about 0.4% manganese and about .0S-0.3% total of iron andsilicon in amounts up to about 0.2% each.

8. The article of claim 7 in TSXX temper, and ex- -hibiting at least 50%greater fracture toughness than conventional 2024T85L 9. The article ofclaim 8 in the form of plate, having a short transverse yield strengthof about 45,000 to about 60,000 p.s.i.

10. An aluminum base alloy in the form of plate prepared by casting androlling the alloy, including hot rolling the casting, said plateexhibiting substantially single phase structure, having a solid solutionmatrix of copper and magnesium in aluminum and a volume percent ofsecond phase particles not exceeding one percent based on particles thatare visible and resolvable in unetched condition under opticalmagnification up to 1000x, said alloy consisting essentially ofaluminum, copper and up to 2% magnesium, including about 45.5% total ofcopper and magnesium, at least 1.2% magnesium and less than 3.8% copperand about 1.3-1.7% magnesium, in the form of at least 945 P. or higherin homogenized condition.

11. The article of claim 10, said alloy including up to about 0.4%manganese.

12. The article of claim 10, said alloy including up to about 0.25%zirconium.

13. The article of claim 10, said alloy including up to about 0.2%chromium.

14. The article of claim 10, said alloy including up to about 0.2%titanium.

15. The article of claim 10, said alloy including up to about 0.2%silicon.

16. The article of claim 10, said alloy including up to about 0.2% iron.

17. The article of claim 10, said alloy containing about .0S-0.3 totalof silicon and iron.

18. The article of claim 10, said alloy including up to about 0.25 zinc.

19. The article of claim 10, said alloy containing about 2.9-3.7%copper, about 1.3-l.7% magnesium and about 0.l-0.4% manganese.

20. A solution heat treated, cold Worked and artificially aged aluminumbase alloy in -TSXX temper, exhibiting substantially single phasestructure, having a solid solution matrix of copper and magnesium inaluminum and a volume percent of second phase particles not exceedingone percent based on particles that are visible and resolvable inunetched condition under optical magnification up to l000 said alloyconsisting essentially of aluminum, about 0.6-2% magnesium by weight,about 4-5.5% total of copper and magnesium, and up to about 0.4%manganese in an amount effective substantially to saturate its matrix.

21. The alloy of claim 20 containing at least about 1.2% magnesium andless than 3.8% copper.

22. The alloy of claim 20 containing about 2.9-3.7% copper and about1.3-1.7% magnesium, in the form of plate having arLL-T plane strainfracture toughness of at least 35 k.s.i.\/in. and a short transverseyield strength of at least 55 k.s.i.

23. The alloy of claim 20 containing about .0S-0.3% total of silicon andiron.

24. The method of claim 1 including hot rolling the ingot to a platethickness of about 3 inches.

25. The method of claim 1 including hot rolling the ingot to a platethickness of about 6 inches.

26. The method of claim 4 including hot rolling the ingot to platethickness, wherein said cold working includes stretching the plate about2%.

27. The method of claim 4 including hot rolling the ingot to platethickness, wherein said cold working includes stretching the plate about6%.

28. The method of claim 4 including hot rolling the ingot to platethickness, wherein said cold working includes stretching the plate about8%.

29. The article of claim 9 wherein the volume percent of second phaseparticles is only about 0.5%.

References Cited UNITED STATES PATENTS 3,333,989 8/1967 Brown et al14S-12.7 2,252,361 8/1941 Bothmann et al. 75-142 2,228,013 1/1941Matthaes 75-142 RICHARD O. DEAN, -Primary Examiner U.S. Cl. X.R.

UNITED STATES PATENT FFTCE ERTIFMME 0F Gammo 3,826,688 Damd July 3o,1974 Patent No.,I

-lt is certifiedy that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Claim l0 .should read as follows to correct a printing error in thepenultimate line:

10.@ An aluminum base alloy inl the form of plate prepared by castingand rolling the alloy, including hot rolling the casting, said plateexhibiting substantially single phase structure, having a solid solutionmatrix of copper and magnesium in aluminum and a volume percent of second phase particles not exceeding one percent based on' particles thatare visible and resolvable in unetched condition under opticalmagnification up to lOOOX, said alloy consisting essentially ofaluminum, copper and. up to 2% magnesium, including about Vl-5.5% totalof copper and magnesium, at least 1.2% magnesium and less than 3 8%copper, by weight, and having a solidus temperature of at least 945F..or higher in homogenized condition.

Signed and sealed this 29th day of October 1974..

(SEAL) Attest:

McCoy ML. GIBSON JR., c MARSHALL DANN Attesting Officer Commissioner ofPatents

